the answer is -$97 for sure.
! V- X" n& Y k2 W4 {2 w; atvb now,tvbnow,bttvbThink about it this way * F7 b6 B& F7 R: W
1) if the 100 bucks is not a fake one, the store owner will gain $3 ($21-$18)
3 L( f) a D! e% p; x2) Now, the owner discovered that the 100 bucks is fake. You can think this as a lost of $100. therefore the overall gain is $3-$100 = -$97 |